National trends in the prevalence of allergic diseases among Korean adolescents before and during <scp>COVID</scp>‐19, 2009–2021: A serial analysis of the national representative study
Authors: Min Ji Koo, Rosie Kwon, Seung Won Lee, Yong Sung Choi, Youn Ho Shin, Sang Youl Rhee, Chanyang Min, Seong Ho Cho, Stephen Turner, So Young Kim, Jinseok Lee, Seung‐Geun Yeo, Katrina Abuabara, Young Joo Lee, Jae Il Shin, Jung‐Hyun Kim, Jung U. Shin, Dong Keon Yon, Nikolaos G. Papadopoulos
Journal: Allergy (2022)

The impact of coronavirus disease 2019 (COVID-19) on allergic diseases in adolescents is not well described. Although there have been previous studies that examined changes in prevalence 1 year into the pandemic, there is a need for follow-up due to the nature of the infectious disease.1 Therefore, this article will examine the prevalence of allergic diseases among Korean adolescents before and during COVID-19 from 2009 to 2021. The data were accessed from the Korea Youth Risk Behavior Web-based Survey (KYRBS) from 2009 to 2021. KYRBS is a self-reported online survey that monitors health-related behaviors that contribute to the leading cause of death and disability among young adults. The survey employs sample selection methods such as stratified cluster sampling so that the survey thoroughly reflects the entire population.2 The period before the pandemic (2009–2019) was divided into intervals of two or three consecutive years, while each year during the pandemic (2020–2021) was examined individually. They were divided in such a manner to obtain stable estimates for the prevalence. Cases of allergic diseases such as asthma, allergic rhinitis, and atopic dermatitis were included on the basis of having been diagnosed within the past 12 months. Allergic morbidity was defined as having at least one of the three conditions mentioned above.3 The study protocol was approved by the institutional review boards of Sejong University (SJU-HR-E-2020-003) and the Korea Disease Control and Prevention Agency. The prevalence of allergic diseases was stratified against covariates such as age, sex, BMI, residence area, smoking status, alcohol consumption, parents' educational level, economic level, and school performance. This was measured through weighted complex sampling analysis using linear and binary logistic regression models which enabled us to quantitatively grasp the extent of change between each period. SAS version 9.4 (SAS Institute) and SPSS version 26.0 (IBM) were used to perform all the statistical analyses. The bold numbers indicate a significant difference of a two-sided p-value less than a 0.05. There was a total of 840,488 adolescents aged 12–18, with 52.30 percent male and a mean age of 15.08 years (Table S1). The weighted prevalence of allergic morbidity increased from 23.19% (95% CI, 22.93–23.45) from 2009 to 2011 to 25.09% (95% CI, 24.76–25.42) from 2018 to 2019. However, there was a pronounced decrease after the outbreak (βdiff −0.095, 95% CI −0.145 to −0.085; odds ratio [OR] 0.799, 95% CI 0.779–0.820). The weighted prevalence of asthma gradually decreased from 2.23% (95% CI, 2.15–2.31) from 2009 to 2011 to 1.99% (95% CI, 1.90–2.09) from 2018 to 2019, then rapidly decreased after the outbreak (βdiff −0.137, 95% CI −0.288 to −0.110; OR 0.495, 95% CI 0.456–0.538). The weighted prevalence of allergic rhinitis increased from 17.79% (95% CI, 17.54–18.04) from 2009 to 2011 to 20.45% (95% CI, 20.14–20.76) from 2018 to 2019. However, it decreased after the outbreak (βdiff −0.119, 95% CI −0.1698 to −0.108; OR 0.795, 95% CI 0.772–0.818). Similarly, the weighted prevalence of atopic dermatitis remained similar, as it increased slightly from 6.74% (95% CI, 6.61–6.87) from 2009 to 2011 to 6.82 (95% CI, 6.65–6.99) from 2018 to 2019. However, it decreased after the outbreak (βdiff −0.030, 95% CI -0.045 to −0.016; OR 0.927, 95% CI 0.892–0.962). It is observed that the female and overweight or obese subgroups are relatively more vulnerable to allergic diseases (Table 1 and Figure 1). Also, the reduction in atopic dermatitis is modest compared to others because aeroallergen is not the main etiology. These results suggest that the prevalence of allergic diseases decreased during the pandemic, with some exceptions (Table S2). The decrease in the prevalence of asthma, allergic rhinitis, and atopic dermatitis could be interpreted as a result of the pandemic. South Korea announced the first case of COVID-19 in January of 2020, and the number of confirmed cases increased by 20 the following month due to social gatherings. Since, the government has implemented strict public health measures in order to prevent and mitigate the transmission of the virus.4, 5 For example, there have been business hour restrictions, self-isolation measures, social distancing guidelines, mask mandates, nationwide lockdowns, school closures, and vaccination recommendations.4, 5 These acted as physical barriers and environmental complex interactions that blocked direct and/or indirect contact and penetration of allergens, hence decreasing the prevalence of allergic diseases. This result is consistent with other studies from Brazil, India, and Singapore which demonstrated a sustained reduction in asthma admissions during the pandemic as a result of widespread public health measures.1, 6 However, they utilize small and heterozygous samples that only examined 1 year into the pandemic. The strength of this study lies in the utilization of almost one million Korean adolescents. Nevertheless, there are several limitations that should be taken into account. First, the study excluded those who are not enrolled in the public education system. Second, there could be a potential for underdiagnosis during the pandemic due to public reluctance to visit the hospital.7 Third, it was hard to estimate the exact quantity and the extent of influence of each risk factor such as changes in physical as well as mental health. Finally, although questionnaire-based assessments used in our study were reliable for adolescents with allergic diseases (kappa coefficient: 0.48–0.80),8 objective measurements such as pulmonary function tests are advised to verify the severity of the disease. The prevalence of overall morbidity of allergic diseases displayed a continuous increase from 2009 to 2019, followed by a minute decrease after the pandemic (2020–2021). In light of the findings, we would like to encourage continued efforts to monitor allergic diseases in the years to come, even after the pandemic is over. This understanding will provide useful information for establishing future policies in response to a new wave of the pandemic. It is also recommended to conduct follow-up research on COVID-19 infection status and the types and severity of allergic diseases. Word Count: 835. The authors would like to thank Stella Ting (Department of English, University of Toronto, Toronto, Ontario, Canada) for proofreading the manuscript. This research was supported by a grant from the Korea Health Technology R&D Project, through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (grant number: HV22C0233) and National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT; grant number: NRF-2020R1C1C1005293). The funders had no role in the study design, data collection, data analysis, data interpretation, or writing of the report. Dr Katrina Abuabara is a consultant for TARGET RWE. Other authors declare that they have no conflicts of interest. Appendix S1 Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.